In the past, flexible printing plates were mounted directly onto the outer surface of a printing cylinder and used for the printing of ink images on a printing medium. However, because the plates could not be easily moved from one cylinder to another, a separate printing cylinder was often needed for each plate.
To overcome the need to use multiple printing cylinders, printing sleeves were developed on which the plates could be mounted. The sleeves are mounted onto a printing cylinder with the assistance of a pressurized gas, such as compressed air, which is passed in a substantially radial direction through holes in a printing cylinder to expand the sleeve to a limited extent to assist the mounting of the sleeve on the cylinder. When the gas flow stops the sleeve contracts and engages the cylinder. The gas pressure is once again used when it is desired to dismount the sleeve from the cylinder.
An early patent which describes such a printing sleeve and the use of pressurized gas for the mounting and dismounting of the sleeve is the Bass et al. U.S. Pat. No. 3,146,709. The patent discloses a printing sleeve, which is formed, in part, of helically wound paper.
The recently issued Hoage U.S. Pat. No. 4,903,597 describes some of the problems encountered with the early wound tubes.
Some of the prior art wound sleeves apparently did not effectively expand unless high pressure air, substantially higher than the 50-100 psi air generally available in production facilities, was radially conveyed between the sleeve and the printing cylinder to facilitate the mounting and dismounting operation. The expandability problem was believed to be due to the thickness of the sleeve walls and the wound construction. In addition, it was believed that wound sleeves also had leakage problems inherent in their design.
The Hoage patent also describes prior art printing sleeves which are made of a metallic material. The metallic sleeves also are believed to require a thin wall to be readily expandable, i.e., thicknesses of up to only about 0.005". Unfortunately, the required thin wall of the metallic sleeves can cause durability problems.
As a solution to the problem of prior art printing sleeves, the Hoage patent proposed a printing sleeve formed of a laminated polymeric material reinforced with a woven fabric which was wrapped around a core to form the sleeve.
The printing sleeve of the Hoage patent can be relatively expensive to make and in some instances it may not expand as well as desired with low pressure air. Therefore, a need still exists for a cylindrically-shaped printing sleeve which is unitary and airtight, and which is readily expandable using a low pressure gas so that it can be easily mounted or dismounted on a printing cylinder.